The invention concerns a device for the voltage adjustment in a self-energized and self-regulated single-phase alternator when said alternator is working at a reduced speed with respect to the rated one.
It is known that especially single-phase alternators, coupled to endothermic motors e.g. alternator traction mortor or engine, not shown, and having a low capacity, for example 1 to 10 kW, are variously used, for example during markets or during open-air maintenance-repairs for which it is necessary to use electric tools and it is difficult to have a nearby electric power supply.
The alternators which are used that way undergo very changeable loads. Generally alternators work mostly loadless because loads are connected just occasionally to them. That is why it is important, in the operation of units using these alternators, to obtain both energetic saving, that is a decrease in the consumption of the alternator traction motor, and a decrease in the air and noise pollution. Therefore it is important that, when the alternators work loadless, their speed is drastically reduced, so that all the polluting emissions, the noise, as well as the fuel consumption, are decreased.
It is known that there are solutions for obtaining the above -mentioned result in alternators in which the adjustment of the current of the alternator inductive circuit is carried out directly, so that the increase or the decrease of the traction motor speed cause proportional increases or decreases of the outgoing voltage. In single-phase alternators the adjustment often is not made directly, but through a capacitor. Said single-phase alternators have a excitation winding placed at 90.degree. with respect to the power winding. The excitation winding is closed on a capacitor.
The function linking the speed of the alternator traction motor to the outgoing voltage in the machines having this type of check is not linear. In fact the result is that, in case of a reduction of the motor speed, a much higher per cent reduction of the voltage is produced, so much that it makes the restart of certain loads impossible. It is important that the voltage is not over-decreased. Sometimes this is necessary because the outgoing voltage of the alternator powers the loads connected to it, as well as the electronic circuits connected to the alternator. Said electronic circuits need a threshold voltage which is not lower than a certain value.
That is why it is important and necessary that the alternator voltage, even if it is reduced because of the decrease of the traction motor speed, has not lower value than the half of the rated voltage or just above. For example in case of an alternator supplying a load at 220 Volt it is important that its loadless and reduced speed voltage is not lower than 100-120 Volt. In order to remedy the above-mentioned drawback single-phase alternators of the known type adjusted through a capacitor either cannot reduce the motor speed or supply a speed reduction at not very low values, just in order to avoid an over-reduction of the outgoing voltage.